Cell senescence is thought to contribute to aging in mammals, and can be induced by critically shortened and thus uncapped telomeres. In humans, telomere shortening accompanies aging, and there is increasing evidence that shortening impairs tissue homeostasis. At the same time, limited proliferation caused by telomere shortening may limit carcinogenesis. Although uncapped telomeres clearly lead to checkpoint responses, questions remain concerning the full range and mechanisms of cellular responses to telomere dysfunction. Here we will investigate new aspects of senescence caused by telomere uncapping in a yeast telomerase mutant model, focusing on epigenetic changes. These will be investigated in three specific aims: 1) Characterize the inhibition of glycolytic gene expression during senescence and the dependence of survivors on glycolytic factors related to an apparent shift of telomere silencing factors to internal genomic loci, including elucidation of the roles of Raplp and sirtuins in these processes, 2) Investigate the relationship between gene expression changes that occur in response to critically shortened telomeres and promoters having sequences with the apparent capacity to form G-quadruplex (G4) DNA, and 3) Determine roles for SUMOylation in regulating the rates of senescence and formation of survivors of senescence. Each of these epigenetic changes has been linked to cell senescence, telomere function, aging and cancer biology in humans, and yeast provides an experimentally tractable model in which to dissect the mechanisms by which they operate. We will use established biochemical, and molecular and cell biological approaches to investigate the functional relationship between the proteins and genomic DNA sequences that mediate the epigenetic changes. All three aims will make extensive use of the Program Cores. In addition, we will collaborate with Dr. Marmorstein (Project 1) to test the effects of small molecule regulators of sirtuins during senescence and in survivors, and with Dr. Berger (Project 2) to compare the roles of chromatin modifications during senescence of telomerase mutants with yeast mother cell replicative aging. Understanding how these epigenetic changes regulate the physiology of cell senescence will offer new insights into aging and cancer biology. Together with the other projects in the program, these studies will provide new targets for the future development of therapeutics aimed at treating age-related diseases and malignancies.